A circuit breaker is an overcurrent protective device that is used for circuit protection and isolation. The circuit breaker provides electrical system protection when a designated electrical abnormality such as an overcurrent event occurs in the system. One type of circuit breaker is a molded case circuit breaker (MCCB), which includes a case containing multiple circuit interrupters of a modular type for multiple poles, commonly for different phases of a three phase electrical system. Typically, the circuit breaker has 3 or 4 poles coupled together with common drive pins.
The circuit interrupt modules are connected by the drive pins to a common drive mechanism for allowing the movable electrical contacts to engage or separate from corresponding stationary electrical contacts in the circuit breaker. The movable electrical contacts are carried on a unitary arm or blade contained on a rotating blade carrier in each module. The common drive pins extend through each of the blade carriers of the separate modules. A common drive mechanism imparts a rotation on the drive pins which in turn rotates the blade carriers to open or close the circuit of all of the poles.
Over time, the operation of the circuit breaker may result in uneven wear of the electrical contacts. For example, after a first occurrence of a short circuit, the electrical contacts associated with either side of the unitary arm or blade of the circuit breaker may begin to erode as a result of arcing from the short circuit which impacts each electrical contact to a different degree. The electrical contacts on one side will tend to have greater erosion than the electrical contacts on the other side. Once the first short circuit begins to unevenly erode the electrical contacts, the side with the greater erosion will likely continue to erode at a faster rate from subsequent short circuits. As a result, the side with the more eroded electrical contacts will have a lower contact force or a diminished or unavailable over travel (also referred to as “overtravel”) range between the movable and stationary electrical contacts when the circuit breaker is in the closed position, even though the less eroded contacts on the other side are still able to establish an electrical connection. The terms “overtravel” and “over travel” as used herein relate to a distance that a movable electrical contact is able to move past an initial contact position between the movable electrical contact and the stationary electrical contact, or a contact force (or magnitude of the force) corresponding to the over travel distance.